Epoxy, cowl hinge, and rivets

A search couldn't find the answer so I post this question:

Do you (1) use fiberglass cloth wetted with epoxy between the hinge and the cowl, or (2) just epoxy thickened with cotton flox and no glass cloth? The bldrs manual on the RV9 describes #(2) but somewhere in there also suggest using fiberglass cloth. If so, what weight cloth?

I suspect thickness of the layer can be a problem if too thick and the hinge halves don't line up properly.

Another concern are the 1/4 inch diameter holes on the thinner alum hinge for added grip. Not much alum left over to the edge of the hinge. Seems like 3/16 dia would be more appropriate.

Lastly, I see some people have used soft rivets for attaching the hinges to the cowl because of cracking caused by the standard hard rivets. Just wondering if I need to place a special order for the softer rivets.

Any experience on these issues would be helpful.

Jim
RV9A

My 2 cents...

I bonded hinge strips once during the build of my -4 (10 years ago) and again about 5 years ago when I had to replace the hinges due to a number of broken eyelets.

• Both times I used standard rivets, though I would have used soft if I had had some on hand
• Neither time did I drill holes in the hinges. In my view, this simply reduces the bonding surface in trade for some additional mechanical interlocking as the adhesive oozes through the holes.
• The second time around, I replaced the rolled hinge supplied with the kit with the extruded version to (hopefully) prevent future eyelet failures. (So far so good)
• I also, purchased a wider hinge section to provide a little more bonding area.
• I used (paste) structural adhesive in lieu of thickened resin or wetted glass. On the second one, I also used an adhesion promoter on the hinges. So far, the strips have remained well adhered.

Good luck,

Thanks Dean for the reply.

I have drilled 1/4" dia holes in the big hinges and 3/16" dia holes in the smaller hinges. I will go with the epoxy w/flox and the hard rivets because thats what I have on hand and what the manual suggest. Going to put vaseline on the ends of the clekos to prevent the epoxy from setting up on them. Once the epoxy fully hardens will pull the clekos out and set the rivets. Thats the plan.

Jim

epoxy

Each has his own style. I am just finishing the cowl (SJ) and I got a ton of advice from many people. My decision was to go with -4 or -5 hinge widths (extruded), have 1/4 holes, one layer of 8 oz cloth between hinge and cowl and then one layer or 8 oz cloth on top of the hinge, the entire "mess" laid up at the same time. I had everything clecoed together and then riveted while still wet. Is that a good idea. I haven't flown yet so time will tell. The advantage of the layer under and on top is that they are bonded through the holes. I did extensive testing of aluminum to epoxy bonding with small samples and suggest you pre-sand the aluminum well with coarse grit. Sand the cowl well in the hinge area before you start. Also throw your clecos into acetone for clean up.
Offset the hinge line from the upper-lower interface.

cowl hinge adhesive

i floxed my hinges and would NOT do it that way again. Epoxy is too brittle on a flexible application. I could hear the epoxy "crack" when working with the cowl after it cured. I would highly suggest using a flexible adhesive, not epoxy.

G-Flex epoxy from West System...

I used West System G-Flex wherever vibration might be an issue...

http://www.westsystem.com/ss/g-flex-epoxy/

from the West System literature
A toughened, versatile, liquid epoxy for permanent waterproof bonding of fiberglass, ceramics, metals, plastics, damp and difficult-to-bond woods. With a modulus of elasticity of 150,000 PSI, it is a bit more flexible than standard epoxies and polyester, but much stiffer than adhesive sealants. This gives G/flex the ability to make structural bonds that can absorb the stress of expansion, contraction, shock and vibration. It is ideal for bonding dissimilar materials. It can be modified with West System fillers and additives, and used to wet-out fiberglass tapes and fabrics. Mixed at a 1:1 ratio, G/flex gives you 45 minutes of working time at room temperature. It reaches an initial cure in 7 to 10 hrs and full cure in 24 hrs.

rv9av8tr said:

i floxed my hinges and would NOT do it that way again. Epoxy is too brittle on a flexible application. I could hear the epoxy "crack" when working with the cowl after it cured. I would highly suggest using a flexible adhesive, not epoxy.

Click to expand...

We used pro seal...